The present disclosure relates generally to entangled photon systems, and more particularly to characterization of operational systems parameters of entangled photon systems.
A method for providing secure transmission of data across a data network involves encrypting the data at the source (sender), transmitting the encrypted data across the data network, and decrypting the encrypted data at the receiver. Reliable methods for encryption/decryption include those that use a secret key known only to the sender and receiver. The issue then arises of how to transmit the key securely between the sender and the receiver.
Optical transmission across optical fibers is widely used in telecommunications networks. Quantum key distribution exploits the quantum physics properties of photons to securely transport keys across an optical network. One method of quantum key distribution encodes information bits in pairs of entangled photons. In each entangled pair, the quantum properties of the individual photons are strongly correlated even when they are separated geographically. In one architecture, a sequence of pairs of entangled photons carrying the information bits for the key are created at a centralized source. For each pair of entangled photons, one photon is transmitted to User 1, and the correlated photon is transmitted to User 2. User 1 and User 2 can individually recover the key from their respective sequence of received photons. Comparison of the quantum states of the photons received by each user can reveal whether a third party has eavesdropped on the quantum key transmission or has substituted a separate quantum key.
Reliable operation of an optical quantum key distribution network requires precise measurements of operational systems parameters. Measurements that can be performed without disconnecting network elements is advantageous for minimizing system downtime.